U.S. patent number 5,374,160 [Application Number 08/255,214] was granted by the patent office on 1994-12-20 for high performance turbomolecular vacuum pumps.
This patent grant is currently assigned to Varian Associates, Inc.. Invention is credited to Marsbed Hablanian.
United States Patent |
5,374,160 |
Hablanian |
December 20, 1994 |
High performance turbomolecular vacuum pumps
Abstract
Turbomolecular vacuum pumps having structures which provide
increased pumping speed, increased discharge pressure and decreased
operating power in comparison with prior art turbomolecular vacuum
pumps. In a first embodiment, the stators of one or more axial flow
vacuum pumping stages in proximity to the exhaust port of the
vacuum pump have progressively lower conductance so that the bulk
velocity of the gas being pumped is increased. In a second
embodiment, one or more stages near the inlet port of the vacuum
pump are provided with a peripheral channel to utilize the
centrifugal component of the gas being pumped. In a third
embodiment, one or more stages in the vacuum pump are molecular
drag stages, each including a disk rotor. One or more pumping
channels in the stator adjacent to the upper surface of the disk
are connected in series with one or more pumping channels adjacent
to the lower surface of the disk. In a fourth embodiment, one or
more stages of the vacuum pump are regenerative stages, each
including a regenerative impeller. Pumping channels in the upper
and lower portions of the stator are connected in series. The
stator channels can be provided with fixed, spaced-apart ribs for
improved performance.
Inventors: |
Hablanian; Marsbed (Wellesley,
MA) |
Assignee: |
Varian Associates, Inc. (Palo
Alto, CA)
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Family
ID: |
25366551 |
Appl.
No.: |
08/255,214 |
Filed: |
June 7, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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875891 |
Apr 29, 1992 |
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Current U.S.
Class: |
415/90;
415/173.1; 415/173.7; 415/182.1; 415/208.1; 415/208.3; 415/208.5;
415/55.1; 415/55.6 |
Current CPC
Class: |
F04D
17/168 (20130101); F04D 19/04 (20130101); F04D
19/042 (20130101); F04D 19/046 (20130101); F04D
23/008 (20130101); F04D 29/542 (20130101) |
Current International
Class: |
F04D
19/04 (20060101); F04D 23/00 (20060101); F04D
17/16 (20060101); F04D 17/00 (20060101); F04D
19/00 (20060101); F04D 29/40 (20060101); F04D
29/54 (20060101); F01D 001/36 () |
Field of
Search: |
;415/90,182.1,173.1,173.7,208.1,208.2,208.3,208.5 ;416/4
;417/423.4 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0043298 |
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Mar 1986 |
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JP |
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1525327 |
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Nov 1989 |
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SU |
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Primary Examiner: Kwon; John T.
Assistant Examiner: Verdier; Christopher
Attorney, Agent or Firm: Fishman; Bella
Parent Case Text
This is a division of the U.S. application Ser. No. 07/875,891,
filed Apr. 29, 1992, still pending.
Claims
What is claimed is:
1. A turbomolecular vacuum pump comprising:
a housing having an inlet port and an exhaust port;
a plurality of axial flow vacuum pumping stages located within said
housing and disposed between said inlet port and said exhaust port,
each of said vacuum pumping stages including a rotor and a stator,
each rotor and each stator having inclined blades;
means for rotating said rotors such that gas is pumped from said
inlet port to said exhaust port; and
means defining a peripheral channel surrounding at least a first
stage of said vacuum pumping stages in proximity to said inlet
port, said peripheral channel including an annular space located
radially outwardly of the inclined blades of the first stage rotor,
the inclined blades of the first stage stator extending into said
peripheral channel such that a centrifugal component of gas flow is
directed through said peripheral channel toward said exhaust
port.
2. A turbomolecular vacuum pump as defined in claim 1 wherein said
peripheral channel has a rectangular cross section in a radial
plane.
3. A turbomolecular vacuum pump as defined in claim 1 wherein said
peripheral channel has a triangular cross section in a radial
plane.
4. A turbomolecular vacuum pump as defined in claim 1 further
including fixed, spaced-apart radial vanes located in the annular
space radially outwardly of the inclined blades of the first stage
rotor.
5. A turbomolecular vacuum pump as defined in claim 1 further
including fixed, spaced-apart inclined vanes located in the annular
space radially outwardly of the inclined blades of the first stage
rotor.
Description
BACKGROUND OF THE INVENTION
This invention relates to turbomolecular vacuum pumps and, more
particularly, to turbomolecular vacuum pumps having structures
which provide increased pumping speed, increased discharge pressure
and decreased operating power in comparison with prior art
turbomolecular vacuum pumps.
Conventional turbomolecular vacuum pumps include a housing having
an inlet port, an interior chamber containing a plurality of axial
pumping stages and an exhaust port. The exhaust port is typically
attached to a roughing vacuum pump. Each axial pumping stage
includes a stator having inclined blades and a rotor having
inclined blades. The rotor and stator blades are inclined in
opposite directions. The rotor blades are rotated at high speed to
provide pumping of gases between the inlet port and the exhaust
port. A typical turbomolecular vacuum pump includes nine to twelve
axial pumping stages.
Variations of the conventional turbomolecular vacuum pump are known
in the prior art. In one prior art vacuum pump, a cylinder having
helical grooves, which operates as a molecular drag stage, is added
near the exhaust port. In another prior art configuration, one or
more of the axial pumping stages are replaced with disks that
rotate at high speed and function as molecular drag stages. A disk
which has radial ribs at its outer periphery and which functions as
a regenerative centrifugal impeller is disclosed in the prior art.
Turbomolecular vacuum pumps utilizing molecular drag disks and
regenerative impellers are disclosed in German Patent No.
3,919,529, published Jan. 18, 1990.
While prior art turbomolecular vacuum pumps have generally
satisfactory performance under a variety of conditions, it is
desirable to provide turbomolecular vacuum pumps having improved
performance. In particular, it is desirable to increase the
compression ratio so that such pumps can discharge to atmospheric
pressure or to a pressure near atmospheric pressure. In addition,
it is desirable to provide turbomolecular vacuum pumps having
increased pumping speed and decreased operating power in comparison
with prior art pumps.
It is a general object of the present invention to provide improved
turbomolecular vacuum pumps.
It is another object of the present invention to provide
turbomolecular vacuum pumps capable of discharging to relatively
high pressure levels.
It is another object of the present invention to provide
turbomolecular vacuum pumps having relatively high pumping
speeds.
It is a further object of the present invention to provide
turbomolecular vacuum pumps having relatively low operating
power.
It is a further object of the present invention to provide
turbomolecular vacuum pumps having high compression ratios for
light gases.
It is still another object of the present invention to provide
turbomolecular vacuum pumps which are easy to manufacture and which
are relatively low in cost.
SUMMARY OF THE INVENTION
These and other objects and advantages are achieved in accordance
with the present invention. According to a first aspect of the
invention, a turbomolecular vacuum pump comprises a housing having
an inlet port and an exhaust port, a plurality of axial flow vacuum
pumping stages located within the housing and disposed between the
inlet port and the exhaust port, each of the vacuum pumping stages
including a rotor and a stator, and means for rotating the rotors
such that gas is pumped from the inlet port to the exhaust port.
Each rotor has inclined blades. One or more relatively high
conductance stators are located in proximity to the inlet port. One
or more relatively low conductance stators located in proximity to
the exhaust port have lower conductance than the high conductance
stators.
The low conductance stators preferably comprise a solid member
having spaced-apart openings to permit gas flow. The openings can
be defined by inclined blades. Alternatively, the low conductance
stators can comprise a circular plate having spaced-apart openings
near its periphery. In a preferred embodiment, a group of low
conductance stators in proximity to the exhaust port has
progressively lower conductance with decreasing distance from the
exhaust port.
According to another aspect of the invention, a turbomolecular
vacuum pump comprises a housing having an inlet port and an exhaust
port, a plurality of axial flow vacuum pumping stages located
within the housing and disposed between the inlet port and the
exhaust port, each of the axial flow vacuum pumping stages
including a rotor and a stator, each stator and each rotor having
inclined blades, and means for rotating the rotors. The vacuum pump
further includes means defining a peripheral channel surrounding at
least a first stage of said vacuum pumping stages in proximity to
the inlet port. The peripheral channel includes an annular space
located radially outwardly of the inclined blades of the first
stage rotor. The inclined blades of the first stage stator extend
into the peripheral channel such that a centrifugal component of
gas flow is directed through the peripheral channel toward the
exhaust port.
Fixed, spaced-apart vanes can be located in the annular space
radially outwardly of the inclined blades of the first stage rotor.
The vanes can lie in radial planes or can be inclined with respect
to radial planes. The vanes prevent backflow through the peripheral
channel and assist in directing gas molecules toward the next stage
in the vacuum pump.
According to a further aspect of the invention, a turbomolecular
vacuum pump comprises a housing having an inlet port and an exhaust
port, a plurality of vacuum pumping stages located within the
housing and disposed between the inlet port and the exhaust port,
each of the vacuum pumping stages including a rotor and a stator,
and means for rotating the rotor such that gas is pumped from the
inlet port to the exhaust port. One or more of the vacuum pumping
stages comprises a molecular drag stage having a rotor comprising a
molecular drag disk and a stator that defines a first channel in
opposed relationship to an upper surface of the disk, a second
channel in opposed relationship to a lower surface of the disk, and
a conduit connecting the first and second channels. The stator of
the molecular drag stage further includes a blockage in each of the
first and second channels so that gas flows in series through the
first channel and the second channel.
In a preferred embodiment, the first and second channels are spaced
inwardly from an outer peripheral edge of the disk so that the
outer peripheral edge of the disk extends into the stator, and
leakage between the first and second channels is limited. In
another embodiment, the first and second channels are annular with
respect to the axis of rotation of the disk and the stator of the
molecular drag stage further includes means defining a third
annular channel in opposed relationship to the upper surface of the
disk and means defining a fourth annular channel in opposed
relationship to the lower surface of the disk. The third annular
channel is connected in series with the first annular channel, and
the fourth annular channel is connected in series with the second
annular channel so that gas flows through the first, second, third
and fourth annular channels in series.
According to yet another aspect of the present invention, one or
more of the vacuum pumping stages of the turbomolecular vacuum pump
comprise a regenerative stage including a rotor and a stator. The
rotor comprises a disk. First spaced-apart rotor ribs are formed in
an upper surface of the disk, and second spaced-apart rotor ribs
are formed in a lower surface of the disk. The disk constitutes a
regenerative impeller. The stator defines a first annular channel
in opposed relationship to the first rotor ribs, a second annular
channel in opposed relationship to the second rotor ribs and a
conduit connecting the first and second annular channels. The
stator of the regenerative stage further includes a blockage in
each of the first and second annular channels so that gas flows in
series through the first annular channel and the second annular
channel.
In a preferred embodiment of the regenerative stage, the first and
second channels are spaced inwardly from an outer peripheral edge
of the disk so that the outer peripheral edge of the disk extends
into the stator, and leakage between the first and second channels
is limited.
According to a further embodiment of the invention, third
spaced-apart rotor ribs are formed in the upper surface of the
disk, and fourth spaced-apart rotor ribs are formed in the lower
surface of the disk. The stator includes third and fourth annular
channels in opposed relationship to the third and fourth rotor
ribs, respectively. The third annular channel is connected by a
conduit to the first annular channel, and the fourth annular
channel is connected by a conduit to the second annular channel.
Gas flows through the first, second, third and fourth annular
channels in series.
According to yet another feature of the invention, the stator
channels of the regenerative stage are provided with spaced-apart
stator ribs. The stator ribs can lie in radial planes or can be
inclined.
According to another aspect of the invention, there is provided a
method for improved vacuum pumping in a turbomolecular vacuum pump
including a housing having an inlet port and an exhaust port, a
plurality of vacuum pumping stages within the housing and disposed
between the inlet port and the exhaust port, each of the vacuum
pumping stages including a rotor and a stator, and means for
rotating the rotors such that gas is pumped from the inlet port to
the exhaust port. The method for improved vacuum pumping comprises
the step of structuring one or more of the vacuum pumping stages
that are located in proximity to the exhaust port for reduced
pumping speed and increased compression ratio relative to the
vacuum pumping stages located in proximity to the inlet port.
BRIEF DESCRIPTION OF THE DRAWINGS
For better understanding of the present invention, together with
other and further objects, advantages and capabilities thereof,
reference is made to the accompanying drawings which are
incorporated herein by reference and in which:
FIG. 1 is a partially broken away, perspective view of a
turbomolecular vacuum pump in accordance with a first aspect of the
present invention, wherein the stators have progressively lower
conductance;
FIG. 2 is a schematic cross-sectional representation of a
turbomolecular vacuum pump similar to the pump of FIG. 1 but with
more stages;
FIG. 3 is an exploded perspective view of the stators for three
stages of the vacuum pump of FIG. 1;
FIG. 4 is a perspective view of an alternative embodiment of a low
conductance stator;
FIG. 5 is a partial cross-sectional view of a turbomolecular vacuum
pump wherein the stators of the first two stages are modified in
accordance with a second aspect of the invention;
FIG. 6 is a fragmentary perspective view of the first stage rotor
and stator of FIG. 5;
FIG. 7 is a partial cross-sectional view of another embodiment of a
turbomolecular vacuum pump wherein the stators of the first two
stages are modified;
FIG. 8 is a fragmentary perspective view of the first stage rotor
and stator of FIG. 7;
FIG. 9 is a fragmentary perspective view of another embodiment of
the pump shown in FIG. 7 wherein radial vanes are provided in the
annular space around the first stage rotor;
FIG. 10 is a fragmentary perspective view in accordance with a
further embodiment of the pump shown in FIG. 7 wherein inclined
vanes are provided in the annular space around the first stage
rotor;
FIG. 11 is a partial cross-sectional view of a turbomolecular
vacuum pump in accordance with a third aspect of the invention
utilizing one or more molecular drag vacuum pumping stages;
FIG. 12 is a cross-sectional plan view of the molecular drag stage
taken along the line 12--12 of FIG. 11;
FIG. 13 is a partial cross-sectional view of the molecular drag
stage taken along the line 13--13 of FIG. 12;
FIG. 14 is a partial cross-sectional view of another embodiment of
a turbomolecular vacuum pump utilizing one or more molecular drag
stages;
FIG. 15 is a cross-sectional plan view of the molecular drag stage
of FIG. 15 taken along the line 15--15 of FIG. 14;
FIG. 16 is a partial cross-sectional view of the upper portion of
the stator taken along the line 16--16 of FIG. 15;
FIG. 17 is an exploded perspective view of a regenerative vacuum
pumping stage showing a regenerative impeller and a lower stator
portion in accordance with a fourth aspect of the invention;
FIG. 18 is a partial cross-sectional view of the vacuum pumping
stage of FIG. 17;
FIG. 19 is a partial cross-sectional plan view of the vacuum
pumping stage taken along the line 19--19 of FIG. 18;
FIG. 20 is a partial cross-sectional view of another embodiment of
the vacuum pumping stage of FIG. 17;
FIG. 21 is a partial cross-sectional elevation view of the
regenerative vacuum pumping stage taken along the line 21--21 of
FIG. 20 and showing gas flow through the upper and lower pumping
channels;
FIG. 22 is a partial cross-sectional view of another embodiment of
the vacuum pumping stage of FIG. 17 wherein the stator channels are
provided with ribs;
FIG. 23 is a partial cross-sectional elevation view of the vacuum
pumping stage taken along the line 23--23 of FIG. 22;
FIG. 24 is an alternate embodiment of the vacuum pumping stage of
FIGS. 22 and 23 wherein the rotor and stator ribs are inclined;
FIG. 25 is an exploded perspective view of a regenerative vacuum
pumping stage, showing a regenerative impeller and a lower stator
portion in accordance with another embodiment of the invention;
FIG. 26 is a partial cross-sectional view of the regenerative
vacuum pumping stage of FIG. 25;
FIG. 27 is an exploded perspective view of a regenerative vacuum
pumping stage wherein the rotor and stator ribs are inclined with
respect to the direction of rotor motion to reduce noise during
operation;
FIG. 28 is a graph showing compression ratio, pumping speed and
input power of the turbomolecular vacuum pump of the present
invention for each vacuum pumping stage; and
FIG. 29 is a graph of throughput of the turbomolecular vacuum pump
of the present invention as a function of inlet pressure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS INVENTION
A turbomolecular vacuum pump in accordance with a first aspect of
the present invention is shown in FIG. 1. A housing 10 defines an
interior chamber 12 having an inlet port 14 and an exhaust port 16.
The housing 10 includes a vacuum flange 18 for sealing of inlet
port 14 to a vacuum chamber (not shown) to be evacuated. The
exhaust port 16 is typically connected to a backing vacuum pump
(not shown). In cases where the turbomolecular vacuum pump is
capable of exhausting to atmospheric pressure, a backing pump is
not required. Located within chamber 12 is a plurality of axial
flow vacuum pumping stages. Each of the vacuum pumping stages
includes a rotor 20 and a stator 22. The embodiment of FIG. 1
includes eight stages. It will be understood that a different
number of stages can be utilized depending on the vacuum pumping
requirements. Typically, turbomolecular vacuum pumps have about
nine to twelve stages.
Each rotor 20 includes a central hub 24 attached to a shaft 26.
Inclined blades 28 extend outwardly from the hub 24 around its
periphery. Typically, all of the rotors have the same number of
inclined blades, although the angle and width of the inclined
blades may vary from stage to stage.
The shaft 26 is rotated at high speed by a motor located in a
housing 27 in a direction indicated by arrow 29 in FIG. 1. The gas
molecules are directed generally axially by each vacuum pumping
stage from the inlet port 14 to the exhaust port 16.
The stators have different structures in different stages.
Specifically, one or more stators in proximity to inlet port 14
have a conventional structure with relatively high conductance. In
the embodiment of FIG. 1, two stages in proximity to inlet port 14
have stators with relatively high conductance. The high conductance
stators 22, as best shown in FIG. 3, include inclined blades 30
which extend inwardly from a circular spacer 32 to a hub 34. The
hub 34 has an opening 36 for a shaft 26 but does not contact shaft
26. In the first two stages of the vacuum pump in proximity to
inlet port 14, the stators 22 usually have the same number of
inclined blades as the rotor 20. The blades of the rotor and the
blades of the stator are inclined in opposite directions.
Starting with the third stage from inlet port 14 and progressing
toward exhaust port 16, stators 40, 42, 44, 46 and 48 have
progressively lower conductance than the high conductance stators
22. Thus, the stators progress from medium conductance in the
middle of the pump to low conductance near exhaust port 16. The
stators 40, 42, 44, 46 and 48 can have any convenient structure
which provides the desired conductance. In the embodiment shown in
FIG. 1, each medium and low conductance stator is fabricated as a
circular plate having openings. The structure of stators 42 and 48
is shown in FIG. 3. In stator 42, a circular stator plate 50 is
provided with inclined openings 52, 54, etc., which simulate the
openings between inclined blades. The stator 42 has eight openings,
and stator 48 has only two openings 56 and 57. In the embodiment
illustrated, the conductance of stators 40, 42, 44, 46 and 48 is
progressively reduced toward exhaust port 16 by progressively
reducing the number of openings in the stator plates.
It will be understood that other structures can be utilized for
providing reduced conductance stators. For example, the inclined
openings 54 in stator plate 50 can be replaced with holes that are
drilled near the outer periphery of stator plate 50. The number
and/or size of the openings in stator plate 50 can be varied to
provide the required conductance. Furthermore, two or more medium
or low conductance stators can have the same conductance to
simplify the fabrication of the pump. The stators 22, 42 and 48
illustrated in FIG. 3 are typically machined from a solid disk.
An alternate stator construction is illustrated in FIG. 4. A stator
58 includes a thin metal plate 60 wherein a central opening 62 and
louvers 64 are formed by stamping. A circular spacer 66 is attached
to the outer periphery of plate 60.
A schematic representation of a turbomolecular vacuum pump similar
to the pump of FIG. 1 but with more stages is shown in FIG. 2.
Rotors 70-80 all include as usual the same number of inclined
blades 82. Stators 86 and 87 in the first two stages near the inlet
port have conventional inclined blades 83. Stators 88-95 have
progressively lower conductance with decreasing distance from
exhaust port 84. It will be understood that the number of stators
having reduced conductance can be varied. Preferably, stators
between about the midpoint of the vacuum pump and the exhaust port
have lower conductance than the stators near the inlet port.
The configuration of the stators shown in FIGS. 1-4 is based on the
fact that the bulk velocity of the gas being pumped is reduced at
the exhaust port 16 in proportion to the compression ratio of the
pump. The flow in the last two or three stages of a conventional
prior art turbomolecular vacuum pump is essentially stagnant. Under
such conditions, the power of the motor is wasted in sloshing the
stagnant gas in and out of the stators. By providing progressively
lower conductance stators in proximity to the exhaust port 16, the
bulk velocity is maintained, the pressure ratio is increased and
the motor power is reduced. Another reason for increasing the bulk
velocity in the higher pressure stages of the vacuum pump is that
the back diffusion of light gases, such as hydrogen and helium, is
decreased. In conventional turbomolecular vacuum pumps, hydrogen
has an easy path for back diffusion across the entire
cross-sectional area of the bladed stages. However, in the
turbomolecular vacuum pump shown in FIG. 1, back diffusion must
occur against the stream of pumped gas (usually water vapor and
air) which has a substantial forward velocity toward the exhaust
port 16. Furthermore, back diffusion must occur through the small
holes in each stator which may have 100 times lower cross-sectional
area than prior art stators.
A second aspect of the invention is shown in FIGS. 5 and 6. The
first few stages of a turbomolecular vacuum pump in proximity to
the inlet port are illustrated. A pump housing 100 has an inlet
port 102. A first pumping stage includes a rotor 104 and a stator
110. A second pumping stage includes a rotor 106 and a stator 112.
The first stage rotor 104 and the second stage rotor 106 are
attached to a shaft 108 for high speed rotation about a central
axis. The first stage stator 110 and the second stage stator 112
are mounted in fixed positions relative to housing 100. The rotors
104 and 106 and the stators 110 and 112 each have multiple inclined
blades. As discussed above, in connection with FIG. 1, the blades
of rotors 104 and 106 are inclined in an opposite direction from
the blades of stators 110 and 112.
In the embodiment of FIGS. 5 and 6, a peripheral channel 114
surrounds the first stage and a peripheral channel 116 surrounds
the second stage. The peripheral channels 114 and 116 have the same
configuration and function in the same manner. Thus, only channel
114 will be described. The peripheral channel 114 includes an
annular space 118 located radially outwardly of first stage rotor
104. The blades of first stage stator 110 extend into and contact
the wall of peripheral channel 114. In the embodiment of FIGS. 5
and 6, the peripheral channel 114 has a triangular cross-section in
a radial plane. Depending on the structure of the pump, the
peripheral channels 114 and 116 can be considered as defined by the
stator structure or as defined by the housing. Relatively small
clearances are provided between housing 100 and rotor 104 and
between housing 100 and rotor 106 at the upper and lower edges,
respectively, of peripheral channel 114. This configuration
prevents reverse flow of gas through channel 114 toward the inlet
port 102.
As indicated above, the gas flow through a turbomolecular vacuum
pump utilizing axial pumping stages is generally parallel to the
axis of rotation. However, the gas flow has a centrifugal velocity
component. The vacuum pump shown in FIGS. 5 and 6 and described
above utilizes the centrifugal velocity component to increase
pumping speed. Gas molecules entering the peripheral channels 114
and 116 as a result of centrifugal movement are directed to the
next stage. Gas molecules near the tips of the inclined blades of
rotor 104 have a centrifugal component and move radially outwardly
into peripheral channel 114. The molecules are then directed
downwardly through stator 110 by the angled inside surface of
peripheral channel 114.
An alternate embodiment of a turbomolecular vacuum pump which
utilizes the centrifugal component of gas velocity is shown in
FIGS. 7 and 8. A pump housing 130 has an inlet port 132. A first
pumping stage includes a rotor 134 and a stator 136. A second
pumping stage includes a rotor 138 and a stator 140. A peripheral
channel 142 surrounds the first stage, and a peripheral channel 144
surrounds the second stage. The peripheral channel 142 includes an
annular space 146 radially outwardly of rotor 134. The inclined
blades of stator 136 extend into and contact the wall of peripheral
channel 142. In the embodiment of FIGS. 7 and 8, the peripheral
channel 142 has a rectangular cross-section in a radial plane. The
peripheral channels 142 and 144 operate generally in the same
manner as peripheral channels 114,116 described above.
It will be understood that the number of stages having peripheral
channels to utilize the centrifugal component of gas velocity is
optional. Typically, one or two stages in proximity to the inlet
port of the vacuum pump are provided with peripheral channels as
described above.
Another embodiment of the pump configuration of FIGS. 7 and 8 which
utilizes the centrifugal component of gas velocity is shown in FIG.
9. The peripheral channel 142 is provided with fixed, spaced-apart
vanes 150 in the annular space 146 around rotor 134. In the
embodiment of FIG. 9, the vanes 150 lie in radial planes that pass
through the axis of rotation of the rotors. The vanes 150 extend
from the upper edges of the inclined blades of stator 136.
Yet another embodiment of the pump configuration of FIGS. 7 and 8
which utilizes the centrifugal component of gas velocity is shown
in FIG. 10. Fixed, spaced-apart vanes 154 are positioned in the
annular space 146 around rotor 134. In the embodiment of FIG. 10,
the vanes 154 are inclined with respect to radial planes that pass
through the axis of rotation. Inclined vanes 154 extend from the
upper edges of the blades of stator 136.
The fixed vanes 150 and 154 in the peripheral channel 142 tend to
direct gas molecules having a centrifugal velocity component
downwardly through the stator to the next stage and prevent
backflow of gas molecules through the peripheral channel 142. In
general, the peripheral channel around one or more stages near the
inlet port of the pump can have any convenient cross-sectional
shape that tends to direct gas molecules toward the next stage. The
housing or stator should be configured at the upper and lower edges
of the peripheral channel to nearly contact the respective rotors
and thereby prevent backflow of gas toward the inlet port.
A third aspect of the invention is illustrated in FIGS. 11-13. One
or more axial flow vacuum pumping stages of a conventional
turbomolecular vacuum pump are replaced with molecular drag stages.
In the molecular drag stage, the rotor comprising a disk and the
stator is provided with channels in closely spaced opposed
relationship to the disk. When the disk is rotated at high speed,
gas is caused to flow through the stator channels by the molecular
drag produced by the rotating disk.
Referring to FIGS. 11-13, a molecular drag stage in accordance with
the invention includes a disk 200, an upper stator portion 202 and
a lower stator portion 204 mounted within a housing 205. The upper
stator portion 202 is located in proximity to an upper surface of
disk 200, and lower stator portion 204 is located in proximity to a
lower surface of disk 200. The upper and lower stator portions 202
and 204 together constitute the stator for the molecular drag
stage. The disk 200 is attached to a shaft 206.
The upper stator portion 202 has an upper channel 210 formed in it.
The channel 210 is located in opposed relationship to the upper
surface of disk 200. The lower stator portion 204 has a lower
channel 212 formed in it. The channel 212 is located in opposed
relationship to the lower surface of disk 200. In the embodiment of
FIGS. 11-13, the channels 210 and 212 are circular and are
concentric with the disk 200. The upper stator portion 202 includes
a blockage 214 of channel 210 at one circumferential location. The
channel 210 receives gas from the previous stage through a conduit
216 on one side of blockage 214. The gas is pumped through channel
210 by molecular drag produced by the rotating disk 200. At the
other side of blockage 214, a conduit 220 formed in stator portions
202 and 204 interconnects channels 210 and 212 around the outer
peripheral edge of disk 200. The lower stator portion 204 includes
a blockage 222 of lower channel 212 at one circumferential region.
The lower channel 212 receives gas on one side of blockage 222
through conduit 220 from the upper surface of disk 200 and
discharges gas through a conduit 224 on the other side of blockage
222 to the next stage.
The operation of the molecular drag stage of FIGS. 11-13 will now
be described. Gas is received from the previous stage through
conduit 216. The previous stage can be a molecular drag stage, an
axial flow stage, or any other suitable vacuum pumping stage. The
gas is pumped around the circumference of upper channel 210 by
molecular drag produced by rotation of disk 200. The gas then
passes through conduit 220 around the outer periphery of disk 200
to lower channel 212. The gas then is pumped around the
circumference of lower channel 212 by molecular drag and is
exhausted through conduit 224 to the next stage or to the exhaust
port of the pump. Thus, upper channel 210 and lower channel 212 are
connected such that gas flows through them in series. As a result,
the molecular drag stage of the present invention provides a higher
compression ratio than prior art stages which operate in
parallel.
According to a further feature of the molecular drag stage, the
upper channel 210 and the lower channel 212 are preferably spaced
inwardly from the outer peripheral edge of disk 200. With this
configuration, an outer peripheral portion 228 of disk 200 extends
into stator portions 202 and 204, thereby limiting leakage between
channels 210 and 212 around the outer edge of disk 200, except
through conduit 220. It will be understood that the radial position
of channels 210 and 212 is a tradeoff between two opposing factors.
It is desired to position the channels 210 and 212 as close as
possible to the outer periphery of disk 200 for high rotational
velocity and, consequently, higher pumping speed. Conversely, it is
desirable to position channels 210 and 212 inwardly from the outer
edge of disk 200 to reduce leakage between channels 210 and 212. It
will be understood that the channels 210 and 212 can be positioned
at the outer periphery of disk 200 within the scope of the
invention. However, in this case the allowable spacing between
rotor and stator must be reduced to limit leakage, thereby reducing
tolerances and increasing cost.
Channels 210 and 212 are shown in FIGS. 11-13 as having rectangular
cross sections. It will be understood that any practical
cross-sectional shape can be utilized within the scope of the
present invention. Furthermore, channels 210 and 212 are not
necessarily equal in shape or size. The primary requirement is that
the upper and lower channels 210 and 212 be connected in series for
high compression ratio and that leakage between the channels be
limited.
An alternate embodiment of the molecular drag stage in accordance
with the invention is shown in FIGS. 14-16. The molecular drag
stage includes a disk 240, an upper stator portion 242, and a lower
stator portion 244 mounted within a housing 245. The disk 240 is
attached to a shaft 246 for rotation about a central axis. In the
embodiment of FIGS. 14-16, the upper stator portion 242 defines an
outer channel 250 and an inner channel 252, which are preferably
circular and concentric. The upper stator portion 242 includes a
blockage 254 in inner channel 252, and a blockage 256 in outer
channel 250. Gas enters inner channel 252 from the previous stage
through a conduit 258 located on one side of blockage 254. On the
other side of blockage 254, a conduit 260 connects inner channel
252 to outer channel 250. The conduit 260 is located adjacent to
blockage 256 in outer channel 250. On the other side of blockage
256, a conduit 262 connects channel 250 in upper stator portion 242
to an outer channel in the lower stator portion 244. Lower stator
portion 244 includes an outer channel 268 and an inner channel 270,
which are preferably circular and concentric. The channels 268 and
270 have the same configuration as channels 250 and 252.
In operation, gas enters the molecular drag stage from the previous
stage through conduit 258. The previous stage can be another
molecular drag stage, an axial flow stage, or any other suitable
vacuum pumping stage. The gas is pumped through channel 252 by
molecular drag produced by the rotation of disk 240 and then passes
through conduit 260 to outer channel 250. The gas is similarly
pumped through outer channel 250 by molecular drag to conduit 262.
The gas then passes through conduit 262 around the outer edge of
disk 240 to outer channel 268 in lower stator portion 244. The gas
is pumped through outer channel 268 and then through inner channel
270 by molecular drag and is discharged to the next stage, or to
the exhaust port of the vacuum pump.
The molecular drag stage of FIGS. 14-16 functions by serially
pumping gas through channels 252, 250, 268 and 270 with a single
rotating disk 240. The molecular drag stage of FIGS. 14-16 thus
provides a high compression ratio.
As discussed above in connection with FIGS. 11-13, the channels 250
and 270 are preferably spaced inwardly from the outer peripheral
edge of disk 240. An outer peripheral edge 280 of disk 240 extends
into stator portions 242 and 244. As a result, the leakage path
between channels 250 and 270 is relatively long and leakage is
limited. The radial position of channels 250 and 270 is a tradeoff
between reducing leakage between the upper and lower surfaces of
disk 240 and maintaining high rotational velocity of disk 240
adjacent to channels 250 and 270. Similarly, selection of the
spacing between channels 250 and 252 and the spacing between
channels 268 and 270 is a tradeoff between limiting leakage between
adjacent channels and maintaining a high rotational velocity of
disk 240 adjacent to the inner channels.
As in the embodiment of FIGS. 11-13, the stator channels 250, 252,
268 and 270 can have any convenient cross-sectional size and shape.
The inner and outer channels are not necessarily the same size and
shape. Three or more stator channels can be utilized adjacent to
each surface of the disk if desired. In general, any practical
number of stator channels can be used adjacent to each surface of
the disk. The gas can be pumped through the channels in the
opposite direction from that shown. The channels are not
necessarily concentric as shown in FIGS. 14-16. According to a
further embodiment, the stator channels adjacent the upper and
lower surfaces of the disk can be spiral rather than circular. The
main requirement of the embodiment shown in FIGS. 14-16 is to
provide a relatively long pumping path on the upper surface of disk
240 and a relatively long pumping path on the lower surface of disk
240, with the pumping paths being connected in series for a high
compression ratio.
A fourth aspect of the present invention is shown in FIGS. 17-19.
One or more axial flow vacuum pumping stages of a conventional
turbomolecular vacuum pump are replaced with regenerative vacuum
pumping stages. A regenerative vacuum pumping stage includes a
regenerative impeller 300 which operates with a stator having an
upper stator portion 302 adjacent to an upper surface of the
regenerative impeller 300, and a lower stator portion 304 adjacent
to the lower surface of the regenerative impeller 300. The upper
stator portion 302 is omitted from FIG. 17 for clarity. The
regenerative impeller 300 comprises a disk 305 having spaced-apart
radial ribs 308 on its upper surface and spaced-apart radial ribs
310 on its lower surface. The ribs 308 and 310 are preferably
located at or near the outer periphery of disk 305. Cavities 312
are defined between each pair of ribs 308, and cavities 314 are
defined between each pair of ribs 310. In the embodiment shown in
FIGS. 17-19, the cavities 312 and 314 have curved contours formed
by removing material of the disk 305 between ribs 308 and between
ribs 310. The cross-sectional shape of the cavities 312 and 314 can
be rectangular, triangular, or any other suitable shape. The disk
305 is attached to a shaft 316 for high speed rotation around a
central axis.
The upper stator portion 302 has a circular upper channel 320
formed in opposed relationship to ribs 310 and cavities 312. The
lower stator portion 304 has a circular lower channel 322 formed in
opposed relationship to ribs 312 and cavities 314. The upper stator
portion 302 further includes a blockage (not shown) of channel 320
in one circumferential location. The lower stator portion in 304
includes a blockage 326 of channel 322 at one circumferential
location. The stator portions 302 and 304 define a conduit 330
adjacent to blockage 326 that interconnects upper channel 320 and
lower channel 322 around the edge of disk 305. Upper channel 320
receives gas from a previous stage through a conduit (not shown).
The lower channel 322 discharges gas to a next stage through a
conduit 334.
In operation, disk 305 is rotated at high speed about shaft 316.
Gas entering upper channel 320 from the previous stage is pumped
through upper channel 320. The rotation of disk 305 and ribs 308
causes the gas to be pumped along a roughly helical path through
cavities 312 and upper channel 320, as best shown in FIGS. 18 and
21. The gas then passes through conduit 330 into lower channel 322
and is pumped through channel 322 by the rotation of disk 305 and
ribs 312. In the same manner, the ribs 312 cause the gas to be
pumped in a roughly helical path through cavities 314 and lower
channel 322. The gas is then discharged to the next stage through
conduit 334.
It will be understood that the shape, size and spacing of ribs 308
and 310 and the size and shape of the corresponding cavities 312
and 314 can be varied within the scope of the present invention.
The principal requirement is for a regenerative impeller having
ribs on its upper and lower surfaces, and corresponding pumping
channels in the stator which are connected so that gas is pumped in
series through the upper stator channel and the lower stator
channel to provide a high compression ratio.
Another feature of the regenerative vacuum pumping stage is
illustrated in FIG. 20. Like elements in FIGS. 18 and 20 have the
same reference numerals. The disk 305 is preferably provided with
an extended lip 340 at its outer periphery. The lip 340 extends
radially outwardly from ribs 310 and 312 into a groove 342 in
stator portions 302 and 304. As in the case of the molecular drag
stages described above, the lip 340 and the groove 342 limit
leakage between upper channel 320 and lower channel 322 by
providing a relatively long leakage path between these channels. As
in the case of the molecular drag stage, it is desirable to
position ribs 308 and 310 and corresponding channels 320 and 322 as
near as possible to the outer periphery of disk 300, while
minimizing leakage between upper channel 320 and lower channel
322.
Another embodiment of the regenerative vacuum pumping stage of
FIGS. 17-19 is shown in FIGS. 22 and 23. Like elements in FIGS.
17-19, 22 and 23 have the same reference numerals. The regenerative
impeller 300 shown in FIG. 22 has the same construction as shown in
FIG. 17, including disk 305 with ribs 308 and 310. The upper
channel 320 in stator portion 302 is provided with fixed,
spaced-apart radial stator ribs 350. Similarly, the lower channel
322 in stator portion 304 is provided with fixed, spaced-apart
radial stator ribs 352. Cavities 354 are defined between ribs 350,
and cavities 356 are defined between ribs 352. The stator ribs 350
and 352 reduce reverse flow through channels 320 and 322,
respectively.
Another embodiment of the regenerative vacuum pumping stage of
FIGS. 22 and 23 is shown in FIG. 24. A regenerative impeller disk
360 is provided with ribs 362 on an upper surface near the outer
periphery thereof and ribs 364 on a lower surface near the outer
periphery thereof. The ribs 362 and 364 are inclined with respect
to radial planes. An upper stator portion 366 defines an upper
channel 368 in opposed relationship to ribs 362. Fixed,
spaced-apart ribs 370 are located in upper channel 368. A lower
stator portion 372 defines a lower channel 374 in opposed
relationship to ribs 364. Fixed, spaced-apart ribs 376 are located
in lower channel 374. The ribs 370 and 376 are inclined with
respect to radial planes. Ribs 370 are inclined in an opposite
direction with respect to ribs 362. Ribs 376 are inclined in an
opposite direction with respect to ribs 364. The configuration of
ribs shown in FIG. 24 provides the advantages described above. The
stator ribs shown in FIGS. 22 to 24 can be used in a configuration
wherein the upper and lower channels are connected in series.
Alternatively, the stator ribs can be utilized in a configuration
wherein the upper and lower channels are connected in parallel.
Another embodiment of the regenerative vacuum pumping stage in
accordance with the present invention is shown in FIGS. 25 and 26.
The regenerative stage includes a regenerative impeller 400, an
upper stator portion 402 adjacent to an upper surface of impeller
400 and a lower stator portion 404 adjacent to a lower surface of
impeller 400. The regenerative impeller 400 includes a disk 405
having spaced-apart radial ribs 408 in a circular pattern at or
near the outer periphery of disk 405 and spaced-apart radial ribs
406 in a circular pattern spaced inwardly from ribs 408. Similarly,
the lower surface of disk 405 is provided with spaced-apart radial
ribs 410 at or near the outer periphery of disk 405 and
spaced-apart radial ribs 412 in a circular pattern spaced inwardly
from ribs 410. The disk 405 is provided with an outer peripheral
lip 414 to reduce leakage between the upper and lower surfaces of
disk 405.
The upper stator portion 402 defines a circular pumping channel 418
in opposed relationship to ribs 406 and a circular pumping channel
420 in opposed relationship to ribs 408. The lower stator portion
404 defines a circular pumping channel 422 in opposed relationship
to ribs 410 and a circular pumping channel 424 and opposed
relationship to ribs 412. The upper stator portion 402 includes
blockages (not shown) in channels 418 and 420, respectively.
Similarly, lower stator portion 404 includes blockages 430 and 432
in pumping channels 422 and 424, respectively. The pumping channel
422 is provided with spaced-apart, radial stator ribs 423, and the
pumping channel 424 is provided with spaced-apart, radial stator
ribs 425. The pumping channels 418 and 420 in upper stator portion
402 have similar spaced-apart, radial stator ribs. The stator ribs
in the pumping channels reduce reverse leakage. The outer
peripheral lip 414 of disk 405 extends into a circular groove 426
in upper stator portion 402 to reduce leakage between the upper and
lower surfaces of disk 405.
A conduit 434 through upper stator portion 402 provides inlet to
channel 418 from a previous stage. A conduit 436 through upper
stator portion 402 interconnects channels 418 and 420. A conduit
440 through stator portions 402 and 404 interconnects channels 420
and 422 around the outer peripheral edge of disk 405. A conduit 442
through lower stator portion 404 interconnects channels 422 and
424. A conduit 444 through lower stator portion 404 interconnects
the regenerative stage to the next vacuum pumping stage or to the
exhaust port of the vacuum pump.
In operation, gas enters the regenerative vacuum pumping stage
through conduit 434 from the previous stage and is pumped through
circular channel 418 to conduit 436. The gas is then pumped through
circular channel 420 and conduit 440 to channel 422 on the lower
surface of disk 405. After the gas is pumped through circular
channel 422, it passes through conduit 442 and is pumped through
circular channel 424. Finally, the gas is exhausted through conduit
444 to the next stage. The regenerative vacuum pumping stage shown
in FIG. 26 provides serial vacuum pumping through four pumping
channels in series. Each channel has a regenerative configuration
using a single regenerative impeller 400. As a result, the
regenerative stage of FIG. 26 provides a high compression
ratio.
The ribs in the rotor and the stator of the regenerative stage of
FIGS. 25 and 26 can be varied as to size (height) and shape within
the scope of the present invention. It will be understood that a
different number of pumping channels can be utilized. For example,
one of the pumping channels shown in FIGS. 25 and 26 can be omitted
to provide a three channel regenerative stage, or more than four
pumping channels can be utilized. The principal requirement is that
the pumping channels be connected in series for a relatively high
compression ratio.
Another embodiment of the regenerative vacuum pumping stage in
accordance with the present invention is shown in FIG. 27. The
embodiment of FIG. 27 is similar to the embodiment of FIGS. 22 and
23, except that the rotor ribs and the stator ribs are inclined
with respect to the direction of rotor rotation for smoother
pumping action and to reduce noise. A regenerative impeller 500
operates with a rotor including an upper stator portion (not shown)
adjacent to an upper surface of the regenerative impeller 500 and a
lower stator portion 504 adjacent to a lower surface of the
regenerative impeller 500. The upper stator portion is omitted from
FIG. 27 for clarity. The regenerative impeller 500 comprises a disk
505 having spaced-apart rotor ribs 508 on its upper surface, and
spaced-apart rotor ribs 510 (shown in phantom in FIG. 27) on its
lower surface. The rotor ribs 508 and 510 are preferably located at
or near the outer periphery of disk 505. Cavities 512 are defined
between each pair of rotor ribs 508, and cavities (not shown) are
defined between each pair of rotor ribs 510. The cavities between
ribs 508 and 510 can have any suitable shape. The disk 505 is
attached to a shaft 516 for high speed rotation around a central
axis.
The lower stator portion 504 has a circular lower channel 522
formed in opposed relationship to ribs 510 and the corresponding
cavities between ribs 510. The lower stator portion 504 further
includes a blockage 524 of channel 522 at one circumferential
location. The lower channel 522 is provided with spaced-apart
stator ribs 526 which define cavities 528 between them. The upper
stator portion has a construction similar to that of lower stator
portion 504. A conduit 530 adjacent to blockage 524 interconnects
the channel in the upper stator portion and lower channel 522
around the edge of disk 505. The lower channel 522 discharges gas
to a next stage through a conduit 532.
The rotor ribs 508 and 510 are inclined with respect to the
direction of rotation of disk 505. Similarly, the stator ribs 526
in lower channel 522 and the stator ribs in the channel of the
upper stator portion are inclined with respect to the direction of
rotation of disk 505. However, the ribs in the stator are inclined
in the opposite direction with respect to the ribs in the rotor so
that the opposed rotor and stator ribs intersect to form X's as
shown in FIG. 27. The inclined ribs in the rotor and stator
channels reduce a momentary interruption of pumping (when the ribs
are aligned) and the generation of noise during operation. The
embodiment of FIG. 27 otherwise operates in a manner similar to the
regenerative vacuum pumping stages shown and described above.
The operating characteristics of turbomolecular vacuum pumps in
accordance with the present invention are illustrated in FIGS. 28
and 29. In FIG. 28, the pumping speed, compression ratio and input
power of each stage in a multistage pump are plotted. The different
stages of the pump are plotted on the horizontal axis, with high
vacuum stages at the left and low vacuum stages at the right. Curve
550 represents the compression ratio and indicates that a low
compression ratio is desired near the inlet port of the pump. The
compression ratio reaches a maximum near the middle of the pump and
decreases near the exhaust port. In general, a high compression
ratio is easy to achieve in molecular flow but is difficult to
achieve in viscous flow. Near the pump inlet port, the compression
ratio is intentionally made low in order to obtain high pumping
speed. After the gas being pumped has been densified, a higher
compression ratio and a lower pumping speed are desired. The
pumping speed is indicated by curve 552. A relatively high
compression ratio is obtained at the higher pressures near the pump
outlet by minimizing leakage, using the techniques described above,
and by increasing the pump power. High pumping speed is not
required near the exhaust port because the gas is densified in this
region. The pump input power is indicated by curve 554. At low
pressures, required power is required mainly to overcome bearing
friction. At higher pressure levels, gas friction and compression
power add to the power consumed by the pump. In general, the
operating point of each stage is individually selected in
accordance with the present invention.
In FIG. 29, the throughput of the turbomolecular vacuum pump is
plotted as a function of inlet pressure. The throughput is
indicated by curve 560. The point at which the throughput becomes
constant is selected as a function of maximum design mass flow and
maximum design power.
While there have been shown and described what are at present
considered the preferred embodiments of the present invention, it
will be obvious to those skilled in the art that various changes
and modifications may be made therein without departing from the
scope of the invention as defined by the appended claims.
* * * * *